In order to prepare for data loss due to disk damage, operation error or virus, the data backup is carried out. By generating copy data by the backup, it is possible to restore data.
In addition, in order to restore data even when the manual backup operation is forgotten, automatic backup is also carried out. Especially, in order to protect the latest state of the data that is frequently updated, the amount of stored data steadily increases.
In order to reduce the amount of data stored by the backup, a differential backup processing to store only added data or changed data is performed. However, even when the differential backup processing is carried out, there is no difference in that the amount of stored data increases every time the differential backup processing is carried out.
Namely, there is no technique to suppress the increase of the amount of backup data stored by the automatic backup.